Synthesis of Anastrozole is reported in U.S. Pat. No. 4,935,437 and European Patent Application EP 0,296,749. The synthetic route mentioned in the said patents suffers a major disadvantage of the formation of Anastrozole regioisomer (2).

To overcome the formation of regioisomer (2), another synthetic route is reported in U.S. Pat. No. 4,935,437; in which compound (3) is reacted with 4-amino-1,2,4-triazole (4) to form quaternary ammonium salt (5), which further undergoes diazotisation reaction to give Anastrozole (1) free from regioisomeric impurity (2) (Scheme—1).

It has been observed that the cyano groups undergo hydrolysis in various conditions to form hydrolysed related compounds.